In the photographic art, a photosensitive element comprising a support carrying a red-sensitive silver halide emulsion having associated therewith a cyan dye developer, a green-sensitive silver halide emulsion having associated therewith a magenta dye developer and a blue-sensitive silver halide emulsion having associated therewith a yellow dye developer is known. Photographic film units are also known in which such photosensitive elements have a diffusion transfer image-receiving element affixed to at least one edge thereof, the diffusion transfer image-receiving element being a support layer which carries an alkaline processing composition permeable and dyeable layer, the image-receiving element and photosensitive element being adapted to be superposed with the support layers being the extremities of the superposed structure.
The basic photosensitive element is taught in U.S. Pat. No. 2,983,606. The element contains a dye developer, i.e., a dye which is a silver halide developing agent, and a silver halide emulsion, and can be exposed to actinic radiation and wetted by a liquid processing composition by immersion, coating, spraying, flowing, etc., in the dark, and the exposed photosensitive element is superposed prior to, during, or after wetting, or a sheet-like support element which may be utilized as an image-receiving element. The liquid processing composition can be applied to the photosensitive element in a substantially uniform layer as the photosensitive element is brought into superposed relationship with the image-receiving layer and, positioned intermediate the photosensitive element and the image-receiving layer, permeates the emulsion to initiate development of the latent image contained therein. The dye developer is immobilized or precipiated in exposed areas as a consequence of the development of the latent image. In unexposed and partially exposed areas of the emulsion, the dye developer is unreacted and diffusible and thus provides an imagewise distribution of unoxidized dye developer dissolved in the liquid processing composition, as a function of the point-to-point degree of exposure of the silver halide emulsion. At least part of this imagewise distribution of unoxidized dye developer is transferred, by diffusion, to a superposed image-receiving layer or element, said transfer substantially excluding oxidized dye developer. The image-receiving element receives a depthwise diffusion from the developed emulsion of unoxidized dye developer without appreciably disturbing the imagewise distribution thereof to provide the reversed or positive color image of the developed image. The image-receiving element can contain agents adapted to mordant or otherwise fix the diffused, unoxidized dye developer. In one embodiment, the desired positive image is revealed by stripping the image-receiving layer from the photosensitive element at the end of a suitable imbibition period.
The dye developers are compounds which contain both the chromophoric system of a dye and also a silver halide developing function of the same molecule. By "a silver halide developing function" is meant a grouping adapted to develop exposed silver halide. A preferred silver halide development function is a hydroquinonyl group. Other suitable developing functions include ortho-dihydroxyphenyl and ortho- and para-amino substituted hydroxyphenyl groups. In general, the development function includes a benzenoid developing function, i.e., an aromatic developing group which forms quinonoid or quinone substances when oxidized.
Multicolor images may be obtained using color image-forming components such as, e.g., the previously mentioned dye developers, in diffusion transfer processes by several techniques. One such technique involves utilizing dye developers by employment of an integral multilayer photosensitive element, as disclosed in U.S. Pat. No. 2,983,606, wherein at least two selectively sensitized photosensitive strata superposed on a single support are processed simultaneously and without separation, with a single, common image-receiving layer. A suitable arrangement of this type comprises a support carrying a red-sensitive silver halide emulsion stratum, a green-sensitive silver halide emulsion stratum and a blue-sensitive silver halide emulsion stratum, the emulsions having associated therewith, respectively, e.g., a cyan dye developer, a magenta dye developer and a yellow dye developer. The dye developer may be utilized in the silver halide emulsion layer, e.g., in the form of particles, or it may be employed as a layer behind the appropriate silver halide emulsion strata. Each set of silver halide emulsion and associated dye developer strata are optionally separated from other sets by suitable interlayers, e.g., by a layer of gelatin or polyvinyl alcohol. In certain instances, it may be desirable to incorporate a yellow filter in front of the green-sensitive emulsion and such yellow dye developer of the appropriate spectral characteristics and capable of functioning as a yellow filter may be employed, and in such instances, a separate yellow filter may be omitted.
The dye developers are dye-image forming materials which are preferably selected for their ability to provide colors that are useful in carrying out subtractive color photography, i.e., the previously mentioned cyan, magenta and yellow. The dye developers employed may be incorporated in the respective silver halide emulsion or, in a preferred embodiment, in a separate layer behind the respective silver halide emulsion. Specifically, the dye developer may, e.g., be in a coating or layer behind the respective silver halide emulsion and such a layer of dye developer may be applied by use of a coating solution containing about 0.5 to 8% by weight of the respective dye developer distributed in a film-forming natural, or synthetic, polymer, such as gelatin, polyvinyl alcohol, and the like, adapted to be permeated by the chosen diffusion transfer fluid processing composition.
An extensive compilation of specific dye developers particularly adapted for employment in photographic diffusion transfer processes is set forth in aforementioned U.S. Pat. No. 2,983,606 and in the various copending U.S. applications referred to in that patent and also in U.S. Pat. Nos. 2,983,605; 2,992,106; 3,047,386; 3,076,808; 3,076,820; 3,077,402; 3,126,280; 3,131,061; 3,134,762; 3,134,765; 3,135,604; 3,135,605; 3,135,606; 3,135,734; 3,141,772, 3,142,565; 3,563,739; 3,551,406; 3,597,200, 3,482,972 and 3,705,184.
It should be understood that the dye developers may contain the specified color initially or the spectral absorption may be temporarily shifted, particularly if the dye developer is disposed in the emulsion layer. The term "dye developer" as used herein is intended to include color shifted dye developers as well as those possessing initially the desired absorption over a given spectral range.
It is preferred that the dye developer be retained in gelatin, however, other natural and synthetic materials may also be employed.
U.S. Pat. No. 3,362,819 teaches image-receiving elements particularly adapted for employment in the preceding diffusion transfer processes which comprise a support layer possessing on one surface thereof, in sequence, a polymeric acid layer, preferably an inert timing or spacer layer, and an image-receiving layer adapted to provide a visible image upon transfer to said layer of diffusible dye image-forming substance.
Silver halide emulsions having a relatively high iodine content, i.e., at least 3 mole percent iodine, generally provide good results when used as the blue-sensitive halide emulsion in the photosensitive elements and film units described above. However, silver halide emulsions which have relatively low iodine content, i.e., less than about 2 mole percent, and which have not been spectrally sensitized, have limited response to longer blue wave length radiation. It is therefore usually necessary to spectrally sensitize such emulsions in order to adjust the sensitivity distribution of the emulsion. Spectral sensitizers can also be used to increase the speed of the emulsion. Without such sensitizers, the response of the emulsion to radiation having a wave length between about 460 and 500 nm is less than desired.
For some time, those skilled in the art have been aware of thiacyanine sensitizers which are generic to the blue sensitizers used in the present invention. In this connection, note should be taken of British Pat. No. 1,252,066 and U.S. Pat. No. 3,177,210. The use of similar sensitizers in a color coupling system is taught by U.S. Pat. No. 3,847,613.
Prior to the present invention, some of the preferred thiacyanine sensitizers were those of copending application Ser. No. 297,456 filed Oct. 13, 1972 now abandoned and replaced by continuation application Ser. No. 766,225, filed Feb. 7, 1977 and represented by the formula: ##STR1## wherein R.sup.1 is a lower alkyl group, i.e., 1-4 carbon atoms; R.sup.2 and R.sup.3 are alkyl, alkoxy, halogen or hydrogen, and the alkylene group contains between 1 and 18 carbon atoms inclusive.
Within this group, a particularly interesting material is: ##STR2## anhydro 5-chloro-3'-ethyl-3-(4-sulfobutyl)-thiacyanine hydroxide (hereinafter referred to as "compound I"). As shown below, in Table 1 compound I can extend the blue sensitivity to 478 nm with a maximum at 465 nm. The sensitivity at the maximum is equivalent to the intrinsic as measured on the wedge spectrogram. Moreover, this sensitizer imparts a good speed to the emulsion.
While compound I is a superior blue sensitizer, it is not without its deficiencies. The response of compound I sensitized low iodide emulsions to radiation of 479 to 500 nm is limited. Also, in order to obtain good color reproduction, the blue speed of the color film must be balanced against the green speed. Some yellow dye developers require a faster blue emulsion to properly control dye transfer.
By employing some of the thiacyanines of formula A other than compound I (i.e., by varying the R.sup.1, R.sup.2, R.sup.3 and alkylene moieties), it has been found possible to increase the extent of sensitivity. It has not been found possible, however, to achieve any greater speed with such other thiacyanine dyes of formula A than is achieved with compound I. Moreover, the use of such other thiacyanine dyes is often accompanied by a loss in the maximum density of the dye transfer wedge obtained from the emulsion (hereinafter D-max) and such a decrease in D-max can be due to fog in the emulsion.
As is apparent from the foregoing, there is still a need for an improved blue sensitizer which can extend the blue sensitivity to as close to 500 nm as possible without a loss in D-max while simultaneously imparting an increased speed to the emulsion and yet facilitating attaining the desired balance between the speed of the green and blue emulsions, and which also exhibits an increased immunity to sensitivity loss in the presence of emulsion stabilizers. Since the green region begins at 501 nm, it is also apparent that such sensitizers must also be characterized by exhibiting a sharp cut off of sensitizer effectiveness at 490 to 500 nm. Such a delicate balance of properties is obviously difficult to achieve.
It is the object of this invention to provide such improved blue sensitizers, photosensitive elements and photographic film units containing such sensitizers. This and other objects of the inventions will become apparent from the following detailed description of the invention.